A major part of health care assessment involves the review and analysis of physiological measurements collected and recorded by electronic data sensors. In addition to vital signs, physiological measures can include detailed measurements of organ functions, body fluid chemistry and rates, activity levels, and similar measures, both measured directly and derived.
The type and quality of physiological measures depends greatly on the type and location of the sensor employed. External sensors, such as thermometers, blood pressure cuffs, heart rate monitors, and the like, constitute the most common, and least invasive, form of sensors. However, these sensors are extremely limited in the kinds of information which they are able to collect and encumber the patient with wearing and maintaining an external sensor. On the other extreme, implantable in situ sensors provide the most accurate and continuous data stream through immediate proximity to organs and tissue of interest. However, implantable sensors are invasive and generally require surgery for implantation.
Recent advances in microchip technology have created a new generation of highly integrated, implantable sensors. For instance, PCT Application Nos. PCT/GB99/02389, to Habib et al., filed Jul. 22, 1998, pending, and PCT/GB99/02393, to Habib et al., filed Jul. 22, 1998, pending, respectively describe an implantable sensor chip and treatment regiment, the disclosures of which are incorporated herein by reference. The sensor chip is adapted to receive and rectify incoming electromagnetic signals and to transmit data relating to treatment parameters by wireless telemetry to a receiver external to a body. Similarly, the emerging Bluetooth wireless communication standard, described at http://www.bluetooth.com/developer/specification/specification.asp, proposes a low cost, small form factor solution to short range data communications, potentially suitable for use in implantable sensor technology.
Even though implantable sensor technology is trending towards smaller and more specialized microchip sensors, in humans, these sensors must still be implanted via surgical procedure. Minimally invasive implantation using large bore needles is impracticable because sensors, particularly when embodied using microchip technology, favor a prismatic shape with substantially rectangular cross sections. A large bore needle can cause a core of flesh or skin (or hide, when used in domesticated animals) to form in the pointed tip as the needle is inserted. Cylindrical needles also severely limit solid sensor sizes, shapes and dimensions to only those that can be inserted through a circular bore.
Although current surgical approaches attempt to minimize the size of incision and decree of invasion, implantation is, at best, costly, time-consuming, traumatic, requires multiple instruments and maneuvers, and potentially risky to the patient. Subcutaneous implantable sensors offer the best compromise between in situ sensors and external sensors and are potentially insertable with a simple injection. These sensors are typically implanted below the dermis in the layer of subcutaneous fat. The subcutaneous implantation of solid materials has been described in the prior art as follows.
An insertion and tunneling tool for a subcutaneous wire patch electrode is described in U.S. Pat. No. 5,300,106, to Dahl et al., issued Apr. 5, 1994. The tunneling tool includes a stylet and a peel-away sheath. The tunneling tool is inserted into an incision and the stylet is withdrawn once the tunneling tool reaches a desired position. An electrode segment is inserted into the subcutaneous tunnel and the peel-away sheath is removed. Although providing a tool for subcutaneous implantation, the Dahl device requires an incision into the subcutaneous fat layer and forms an implantation site larger than the minimum sized required by the electrode segment. Further more, the cylindrical bore precludes the injection of non-conforming solid sensors or materials.
An implant system for animal identification that includes a device for implanting an identification pellet in a fat layer beneath the hide or skin of an animal is described in U.S. Pat. No. 4,909,250, to Smith, issued Mar. 20, 1990. The device includes a curved needle-like tube that terminates at a tapered, sharpened point. An elongated, flexible plunger is slidably received within the needle-like tube. The pointed tip is inserted through the hide or skin and the plunger is actuated to drive the identification pellet from the tip into the fat layer. However, the Smith device uses an oversized open bore which can cause coring of the hide or flesh.
A trocar for inserting implants is described in PCT Application No. PCT/US99/08353, to Clarke et al., filed Oct. 29, 1999, pending. An implant retention trocar includes a cannula for puncturing the skin of an animal and an obturator for delivering the implant. A spring element received within the cannula prevents an implant from falling out during the implant process. The cannula has a distal tip design which causes a minimum of trauma and tearing of tissue during implant insertion. However, the distal tip design is specifically directed to cannulas having a substantially circular bore and thereby limits the size and shape of implant which can be inserted through the Clarke trocar.
An instrument for injecting implants through animal hide is described in U.S. Pat. No. 5,304,119, to Balaban et al., issued Apr. 19, 1994. The instrument includes an injector having a tubular body divided into two adjacent segments with a hollow interior bore. A pair of laterally adjacent tines extend longitudinally from the first segment to the distal end of the tubular body. A plunger rod has an exterior diameter just slightly larger than the interior diameter of the tubular body. With the second segment inserted beneath the animal hide, the push rod is advanced longitudinally through the tubular body, thereby pushing the implant through the bore. As the implant and rod pass through the second segment, the tines are forced radially away from each other, thereby dilating or expanding the incision, and facilitating implant. The instrument is removed from the incision following implantation. Though avoiding the coring of animal hide or flesh, the instrument forms an implantation site larger than the minimum sized required by the implant and causes potentially damaging compaction of the implant against the laterally adjacent times during implant delivery.
Therefore, there is need for a non-surgical instrument and method for subcutaneous implantation of sensors and solid materials that preferably does not require an incision preparatory to instrument insertion.
There is a further need for a subcutaneous implantation instrument and method capable of implanting sensors and other solid materials that are not readily disposed to implantation through a substantially circular bore.
Moreover, there is a further need for a subcutaneous implantation instrument and method which is minimally invasive, preferably creating the smallest needed implantation site, and capable of implantation without exposing the implant to longitudinal stresses.